1. Field of the Invention
The present invention relates to projection systems utilizing liquid crystal displays. In particular, it relates to projection television systems.
2. Background of the Disclosure
Rear projection television systems utilizing liquid crystal displays have been proposed. In these known systems, the liquid crystal display consists of a polarizer, the actual liquid crystals, and an analyzer, all packaged as an unit. Light falling on the unit is polarized in a particular plane by the polarizer. This light, herein referred to as first polarized light, then passes through the liquid crystals. Liquid crystals which have been charged, i.e. to which an electrical signal has been applied, rotate the plane when no electrical signal is applied to the liquid crystal, of polarization to a second plane in the presence of such an electrical signal. The light coming from the liquid crystals thus contains light polarized in a first plane and light polarized in a second plane. The analyzer then selects one of the planes, i.e. light polarized in one of the planes will pass through the analyzer, while light polarized in the other plane is blocked. The selected light then passes through a projection lens system and is imaged onto a projection screen.
A major problem with this type of projection arrangement is the lack of contrast resulting from loss of, on the average, 50% of the light in the analyzer. Even standard contrast enhancing techniques, such as blackening the grooves between the lenticulars on the front of the screen, use of diffusers, etc. do not yield a picture having adequate contrast.